1. Field of Invention
The present invention relates to production of specific types of laser light that can be used in analysis of certain systems. In particular, the present invention is directed to methods for splitting up a pulsed laser beam into multiple pulsed beams, each eventually traveling in the same direction to a target. The manipulated pulses may be beneficially used in ultrahigh-speed imaging and other applications.
2. Description of Related Art
Non-intrusive, laser-based optical diagnostic techniques are important in spatially and temporally resolved measurements of turbulent and chemically reacting flow processes such as combustion. In particular, spontaneous Raman scattering (SRS) spectroscopy using pulsed lasers is one of the few techniques that can provide a quantitative measurement of major chemical species concentrations and temperature in turbulent reacting flows. In order to collect high-quality SRS data in gas-phase flows, high-energy pulsed lasers are required to compensate for the weak signal levels generated by the Raman effect.
In the past decade, reliable high energy (and high peak power) Q-switched (QS) Nd:YAG lasers that produce circa 1 J pulses at 532 nm have been used for SRS measurements of gas-phase molecular species. This wavelength output obtained by second harmonic generation (SHG) is a popular choice for SRS excitation and is often used since it maximizes the weak Raman signal with conventional visible-wavelength optics and detectors. However, high energy QS lasers often suffer from laser-induced plasma spark generation at the focused probe volume. The strong optical emission from the plasma spark overwhelms the weak Raman scattering signal, making spatially resolved measurements with high energy QS Nd:YAG lasers very challenging.
Previously, flashlamp-pumped dye lasers, although inconvenient to use, were often employed for SRS excitation since they produced laser pulse energies of order 1 J over several microseconds at 532 nm, avoiding the plasma spark problems inherent with QS Nd:YAG lasers. Note that SRS signal is linearly proportional to the total energy of laser pulse and not the intensity.
Thus, a way of reducing the peak laser power while maintaining the total pulse energy is needed to facilitate SRS measurements in combustion environments using the readily available and convenient QS Nd:YAG laser. Additionally, the processes need to be simple, low cost and relatively compact, and the design parameters of the processes need to be easily optimized to the requirements of particular applications.